1. Field of the Invention
The present invention generally relates to a system for latching the fin covers of a missile having retractable folding fins in the stowed position and for releasing and jettisoning the covers to permit deployment of the fins upon command following launch of the missile.
2. Description of the Related Art
Prior art typically requires one pyro device for each cover being jettisoned. This is costly, especially for a low cost application such as gun launched guided munitions. Prior art also requires wires to be connected to each individual pyrotechnic device.
A key objective of the present invention is to be able to withstand the severe accelerations during gun launch and subsequently to function correctly during flight. It is desired to retain the covers over the canard slots throughout the storage life of the round and during the gun launch as well as in the initial portion of the flight. It is then desired to release the covers upon command from the flight control system and eject them in such a way that the covers do not impact any portion of the vehicle, such as the tail fins, as they are jettisoned. Further, at the time the covers are jettisoned the fins are to unfold from within the vehicle and extend into their flight controlling position in the air-stream.
It is desired to use a single electrically initiated pyrotechnic actuator (pyro device) which, upon electrical command, ignites a propellant charge which pushes a piston. The piston in turn moves the mechanism which first unlatches the covers and then pushes them off.
For convenience the pyrotechnic device, which converts the electrical command signal into force and motion, should be accessible from outside the round after the major portion of the assembly and testing has been completed.
It is desirable to be able to release the covers and extend the fins when the fins and covers are completely stowed and in their storage prelaunch state in order to allow testing and access for any rework found to be necessary at that time. This should be capable of accomplishment by simple hand tools. During this procedure, the pyrotechnic device should be removed from the assembly first as a safety issue prior to other tasks.
It is required that the fins and covers be easily folded and installed, with reasonably simple assembly tools, as part of the normal assembly procedure. Any electrical connections to the pyrotechnic squib actuator should be established more or less automatically as part of the pyrotechnic device installation process. It is critical that these are reliable after being subjected to the launch shock.
The invention is essentially as described in the accompanying Abstract of the Disclosure. In brief, particular arrangements in accordance with the invention incorporate apparatus for the control, storage and deployment of the steering fins of a missile. In storage, these fins are protected by covers which are firmly latched in the stowed position. In such position, the covers serve to prevent the fins from deployment. The system has the capability of withstanding the shocks and high G forces of the launch procedure, including those encountered during launch from a gun which may reach a level of 30,000 G""s. Following launch, arrangements of the invention provide for the immediate and simultaneous release and jettisoning of the covers, followed by deployment of the fins into proper control positions.
The activation of the system of the invention begins with the firing of a pyrotechnic device. As a result, the pyrotechnic pin pushing actuator is caused to extend in response to an electrical command signal. As the pyrotechnic actuator piston extends it pushes a wedge member into a ramped feature in a centrally located spool, causing the central spool to move forward (upward in the drawings), which in turn causes rocker arms that are engaged in an annular groove in the spool to be moved forward on their innermost portion. This causes the arms to rock or pivot about the pivot bearing provided. As the arms pivot, their outer ends, which are provided with latching hooks, are caused to disengage a mating feature provided on the inner side of the slot covers, thus releasing the covers. As the arms continue to rotate, a portion of the latching hook which is designed to provide a camming action on the cover kicks the cover outward. Because the cover is captured temporarily by a hinge at the aft edge, the cover pivots about that hinge. This causes the forward edge of the slot cover to enter the airstream and the dynamic pressure, caused by flight speed, further lifts the cover away from the slot opening. The cover continues to rotate about its aft edge hinge until, at about 20 or 30 degrees of total rotation, the hinge disconnects and the cover is free to fly away from the round.
Particular benefits from the development of the latch and release system of the invention relate to the fact that the latch arms and the actuating spool are mass balanced as a group. This allows the system to withstand the high acceleration loading at launch without inadvertently unlocking. In addition, to further protect from inadvertent unlocking, the central spool is retained by a member that must be sheared by the effect of the wedge driven by the high force from the pyrotechnic actuator before the arms can move.
Assembly of the various components in the apparatus of the invention is a relatively simple procedure. The system is easily assembled during the process of installing the aft-most actuator plate molded housing. The concept for assembly is a simple placement of the four release latch rocker arms in their saddles in the mid-housing and engaging them with the-annular ring in the central spool. All the components are then captured by the aft housing plate as it is attached to the mid plate. The activating wedge which is driven by the pyro actuator is installed later. A tool can be used to reach in through the pyro access port to operate the fin/cover spool and engaged rocker arms to test the release mechanism.
The fins are not retained by the fin/cover release system unless the covers are in place. After deployment or prior to installation of the covers in the assembly procedure, the fins are locked in the extended position by sliding piston/wedges that are driven by springs located inside the fin shafts. To fold the fins a simple hand tool is used to push the fin locking wedge back into the shaft. Meanwhile the fin is pushed toward its folded position until reaching the point, at about 45 degrees of sweep, where the fin can overcome the wedging effect and retract the piston to reach the completely folded position. The fins will need to be retained with a band or similar tool if they are to remain folded prior to the covers being installed.
The covers can be installed after folding the fins using the procedure described above. Because the release mechanism is coupled to all four covers, the covers must be installed simultaneously. The four covers, with molded on O-ring seals, are set in place with their aft edges engaged in the releasing hinge groove. The covers are then simultaneously pressed inward until the latches are fully engaged. A light force spring is provided to help with this procedure by biasing the central spool toward the latched position. At-this point the retaining wedge can be inserted thru the pyro actuator port. If the latches are not fully engaged the wedge cannot be installed. This operation can be accomplished quickly and easily by one person, using only simple tools.
Deploying the covers, with the resulting fin deployment, can be done manually, without using the pyrotechnic device and prior to installing the device, by using the tool mentioned above which reaches through the pyro access port to operate the fin/cover spool and engages the rocker arms which then release and eject the covers. If the pyro device is already installed, it must first be removed by simply unscrewing the retaining fastener and withdrawing the pyro assembly. The unlatching tool is then inserted as before mentioned.
The pyro actuator assembly used in arrangements of the present invention is similar to that used on the Stinger missile to release the fixed wings. The more or less xe2x80x9cstandard pin pusherxe2x80x9d type of assembly is supported in a molded sub-housing that is inserted thru the outer skin and held by a retaining screw. EMI protection and moisture sealing are provided as well.
As with the Stinger missile, the pyro sub-housing is provided with electrical contacts that automatically, at installation, mate with contact pads that provide firing current to the squib when activated. Squib meters and other conventional test equipment can check the squib circuit.
Normally the squib is not fired during testing and therefore replacement of the pyro actuator is a highly unusual event. Because of the high forces involved with the pyro actuator and the retaining member which the pyro actuator is designed to shear during cover release, the aft cover of the CAS (cam actuator system) must be removed to replace the sheared retaining member. This retaining member assures that the covers stay securely fastened during launch setback and set forward loads. Repeating the steps for the assembly mentioned above will be required after any replacement of the retaining member.